Show the following sequence as a monotone increasing

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    Increasing Sequence
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Discussion Overview

The discussion revolves around proving that a given sequence is monotone increasing based on specific conditions provided. The participants explore the implications of the sequence's definition and the role of the supremum of the set from which the sequence is drawn.

Discussion Character

  • Technical explanation, Debate/contested

Main Points Raised

  • One participant presents a sequence defined by the conditions ${x}_{n-1} < x_n \le \sup S$ for all $n \ge 2$ and seeks help in proving it is monotone increasing.
  • Another participant questions whether the condition ${x}_{n-1} < x_n$ already implies that the sequence is monotone increasing, assuming ${x}_{1}$ is defined.
  • A subsequent reply confirms that the assumption about ${x}_{1}$ is correct and inquires if this allows one to conclude the sequence is monotone increasing.
  • Another participant agrees that the strict inequality ${x}_{n-1} < x_n$ indicates strict monotonicity and suggests that the supremum does not affect the proof, questioning if there is something overlooked in the reasoning.

Areas of Agreement / Disagreement

Participants generally agree that the condition ${x}_{n-1} < x_n$ suggests the sequence is monotone increasing, but there is some uncertainty regarding the necessity of the supremum and whether additional proof is required.

Contextual Notes

The discussion does not resolve whether the supremum has any implications for the proof, and the role of ${x}_{1}$ is assumed but not explicitly defined in the initial post.

cbarker1
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Dear Everyone, Here is the sequence: Let $S\subset\Bbb{R}$ and ${x}_{n}\in S$ and $S\ne\emptyset$ . ${x}_{n-1}<{x}_{n}\le\sup S$ for all $n\ge2$. Prove the sequence is monotone increasing.

I need help proving it; I do not know where to start? Thanks
Carter
 
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I'm confused: Isn't this already given since $x_{n-1} < x_n$ for all $n \ge 2$, assuming $x_1$ is the first term in the sequence?
 
The assumption is correct where ${x}_{1}$ is given. So I can say the sequence is monotone increasing?
 
Yes. I mean, you are given terms $x_n$ in a set $S$ such that $x_{n-1} < x_n$ for all $n \ge 2$.
That latter inequality is the definition of strict monotonicity, so if the exercise really reads like this, then I cannot see what you would have to do else. (The supremum does not play any role, either.)

Anyone else here on board that sees something I overlooked?
 

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